[Finally, an understanding of Huntington's disease!]

A beautiful piece of work using extensive single-cell studies illuminates the mechanism of Huntington's disease: the somatic expansion of the (CAG)n tract, very slow at first but accelerating once a critical repeat length is reached, drives extensive changes in gene expression in striatal neurons and eventually leads to cell death and atrophy of the striatum. This explains many puzzling features of the disease and may have important implications for possible therapy and for the understanding of other triplet repeat disorders.